as described in topic, there is a kind of unregular knocking sound.
When starting the engine it runs nice and smooth, and no strange sound at all.
But when itīs getting warmer this knocking sound suddenly appears, sounds a bit like beating metal, but it is not regular at all. The warmer the engine becomes the louder the sound is. When accelerating, the sound disappears.

When shift into D or R the sound changes, but itīs louder. Have a look at my video, there you can hear:

Sometimes things happen even if you never worked there. It's easy enough to remove the inspection cover at the lower end of the engine . Just as you feel you didn't work on the main brgs , it could be involved.There are a few things you might check , crankshaft end ply, torque converter flex plate, crankshaft pulley which sometimes will separate from the bolted section. Whether you worked there or not , the idea is to determine the source of the heavy rumble. I have heard noises like this when spark plug wires were not in the right firing order.
Did you compare the replacement gasket(s) to the ones you removed?
Rod brgs don't produce that heavy rumble , but mains can.